NONMEM Users Network Archive

Hosted by Cognigen

RE: OMEGA BLOCK with mixture model?

From: Mark Sale - Next Level Solutions <mark>
Date: Tue, 14 Apr 2009 08:46:23 -0700

Nele,
 You'll need to rearrange/reassign your ET= As so that you can have correlation between CL(1) and F1, and CL(2) and F1,= but not CL(1) and CL(2).  So, put ETA(1) on CL(1), ETA(2) on F1 and E= TA(3) on CL(2), then $OMEGA like this:

$OMEGA BLOCK(3)
0.1=             &n= bsp;       ;CL(1)
0.01 0.1       &nbs= p;     ;F1
0 =      0.01   0.1  ;CL(2)

This is= the BAND matrix, which is permitted.

Mark Sale MD
Next Level Solutions, LLC
www.NextLevelSolns.com
919-846-9185

-------- Original Message --------
Subject: [NMusers] OMEGA BLOCK with mixture model?
From: nele.plock Date: Tue, April 14, 2009 11:08 am
To: nmusers

Dear all,

I am trying to fit a PK model to oral data. I= n the data, we observed two things: First, CL seems to be negatively correl= ated with F1. Secondly, there seem to be two subpopulations in the exposure= , let's say a large group with 'normal' and a second group with high exposu= re. I would like to identify the subpopulations using a mixture model, but = keep the correlation between CL and F1. Now I ran into problems when coding= the $OMEGA BLOCK.

I f= igured the block to be something like:
$OMEGA BLOCK(3)
0.1  ;CL1
0 FIX 0.1 ;= CL2
0.01 0.01 0.1 ;F1

The error message that appe= ars is:
a covariance is zer= o, but the block is not a band matrix

I assume that this means that I am not allowed to fix the c= orrelation between the two clearance-omegas to zero. However, it would be u= nreasonable to allow a correlation, because the omegas belong to different = subpopulations, so there can't be a correlation. On the other hand, I did n= ot include subpopulations for F1, so how can I keep this correlation to bot= h CL-subgroups?

Any th= oughts on this would be highly appreciated!
Best wishes
Nele
____________________= __________________________________________

Dr. Nele Plock
Phar= macometrics -- Modeling and Simulation

Nycomed GmbH
Byk-Gulden= -Str. 2
D-78467 Konstanz, Germany

Fon: (+49) 7531 / 84 -  = ;4759
Fax: (+49) 7531 / 84 - 94759

mailto: nele.plock com
http://www.nycomed.com

County Court: Fre= iburg, Commercial Register HRB 701257
Chairman Supervisory Board: Charl= es Depasse
Management Board: Dr. Barthold Piening, Gilbert Rademacher, = Dr. Anders Ullman


----------------------------------------------------------------------
Proprietary or confidential information belonging to Nycomed Group may
be contained in this message. If you are not the addressee indicated
in this message, please do not copy or deliver this message to anyone.
In such case, please destroy this message and notify the sender by
reply e-mail. Please advise the sender immediately if you or your
employer do not consent to Internet e-mail for messages of this kind.
Opinions, conclusions and other information in this message that
pertain to the sender's employer and its products and services
represent the opinion of the sender and do not necessarily represent
or reflect the views and opinions of the employer.
----------------------------------------------------------------------

left.letterhead
(image/png attachment: left.letterhead)

Received on Tue Apr 14 2009 - 11:46:23 EDT

The NONMEM Users Network is maintained by ICON plc. Requests to subscribe to the network should be sent to: nmusers-request@iconplc.com.

Once subscribed, you may contribute to the discussion by emailing: nmusers@globomaxnm.com.